Vibrations on an overhead transmission line are typically an aeolian vibration and a galloping. The aeolian vibration is one which is caused by Karman vortex behind the conductor or conductors of the transmission line (referred to as the conductor hereinafter) with respect to the direction of wind to vertically vibrate the conductor of the transmission line with high frequency (such as about 10 to 100 HZ) and with low amplitude (such as about 2cm). Such an aeolian vibration may be prevented by a well known device such as a Stockbridge damper, a torsional damper and a bate damper. On the other hand, the galloping vibration is one which is generally caused by ice and snow collecting on the conductor of the transmission line to vibrate them with low frequency (such as about 0.1 to 1 HZ) and with large amplitude (such as about a few centimeters to ten and extra meters) and such a vibration causes unfavorable accidents such as short-circuit between the phase conductors. The galloping cannot be prevented by the conventional device such as a Stockbridge damper, a torsional damper or a bate damper.
It has been found that the galloping tends to occur when the conductor of the transmission line with ice and snow thereon is blown by wind having the velocity of about 10 to 20 m/s and that it tends to be produced in a severer manner in case of a bundle conductor than in case of a single conductor of the transmission line. It has been also found that it tends to occur in a severer manner in the case of a light conductor such as steel reinforced aluminum conductor (ACSR) than in the case of a weighty conductor such as copper stranded conductor.
Of late, there has been a tendency to use an overhead transmission line of the bundle conductor type because of increased demand of electric power, and in many cases the transmission line has been constructed through a mountainous district which is topographically and meteorologically severe, because of difficulty to find a site to construct it. Thus, more and more transmission lines will exist which tend to produce a galloping. Accordingly, it is required that a damper be developed which can effectively prevent the galloping.
Conventionally, in order to prevent the galloping on the overhead transmission line, the transmission line has been strung so that the phase conductors thereof are largely spaced from each other. However, this has the disadvantage that the expenses are very high for construction of towers, due to the requirement of their sufficient height.
In another prior art arrangement, a line spacer has been used for preventing the galloping. The line spacer comprises an insulating rod or insulator and clamps on either side of the insulator to clamp the ends of the insulator to the conductors of the transmission line, so that it holds the distance between the phase conductors of the transmission line in a forced manner. However, this cannot be used for an extra-high voltage transmission line due to deterioration of insulation of the insulator.